The invention relates to a flame-type heater plug for an air-compression fuel-injection internal-combustion engine, especially a direct-injection and superchargeable internal-combustion engine. Such a heater plug includes a plug housing with a proportioning insert provided for the fuel supply and with a protective tube projecting into the suction pipe of the internal-combustion engine and located in the flow path of the intake air, and a heater tube with a control coil level with the passage orifices arranged in the protective tube and with a heating coil extending approximately as far as the free end of the protective tube.
Flame-type heater plugs serve as a cold-starting aid and as a preheater system to make the diesel fuel more ignitable. They are preheated as a function of the temperature of the internal-combustion engine. For example, at temperatures below 0.degree. C., before starting, since in the starting phase, with the internal-combustion engine cold and the outside temperature low, the heat generated during the high compression would not be sufficient to ignite the fuel. This would result in undue quantities of unburnt fuel mixture and a high soot emission.
The publication "BERU" aktuell", May 1987, issue 11, page IX, discloses a flame-type heater plug, in which a heater tube corresponding to the bar heater plug (see page VII) and with a control and heating coil is arranged in the protective tube or in the flame sleeve. Plugs of this type are self-regulating, that is to say, with an increasing temperature of the heater tube or of the control coil, the current consumption of the heating coil controlled by the control coil decreases.
During starting, fuel flows past the hot heater tube, ignites and heats the intake air flowing past. This ensures a rapid ignition of all the cylinders of the internal-combustion engine. However, a disadvantage which became evident is that, at a high air velocity in the intake pipe, the flame was sometimes blown out and it was therefore impossible to avoid starting difficulties and smoke emissions.
An object on which the invention is based is to provide measures on the above-mentioned flame-type heater plugs which ensure a fault-free operating cycle of the internal-combustion engine during the starting phase even at a high air throughput, especially in supercharged engines.
According to the invention, this object is achieved by an arrangement wherein the heater tube has a lengthened tube part which is arranged without protective tube in the air flow path, and wherein arranged additionally in the lengthened tube part is a control coil which is connected operatively to the heating coil.
As a result of the special design of the lower part of the flame-type heater plug, in which the lengthened heater tube with an additional control coil is located in the flow path of the intake air without protective tube, at high air velocities cooling occurs in this region and leads to an increased current consumption of the heating coil and thus to a temperature rise in the inflammation zone. The result is that the flame is not extinguished even with a high air throughput.
Although a coil subdivided into three portions in the heater tube is known from German Patent Document DE 3,309,133 A1, nevertheless in this coil arrangement there is only one control coil, specifically located between two heating coils. Moreover, the heater tube containing the three portions is arranged entirely in the protective tube of the flame-type heater plug.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.